Chuck,
I would agree with you concerning all types of lengths. I created an English fighting knife to go with my 1860 Colt to represent the 1869 timeframe. Copy of knife on page 92 of the Peacemaker book by Wilson. I estimated the blade at 6 3/4 to 7 inches. It belonged to specific person during a specific time. It was perfect for him.
But in the post I was referring to the Texas Rangers after the 1875 timeframe. I figure that the Rangers were always working with their equipment and that they would have had the most experience with what worked. Plus the interview was from an actual member not just an observer. Therefore the length he stated would be of interest.
I would believe the longer knives you saw would represent the early Rangers, after Texas independence. But this is before the 1860 date that was listed in the first post.
Most of the pictures available in the books used for CAS reference mainly show Texas Ranger after 1875 with what I would call general hunting length knives or daggers. That is why I commented about them. If you have or know of other photos, I would appreciate seeing them.
I think it all depended on the persons desires, needs, likes (just like today) and what the makers had available. What did the makers create and why? Not every knife was a custom order. There are a lot of knives in various lengths shown in the Peacemaker book someone bought or made them for a reason.
If you go to the 1860's time line and the Civil War, then maybe the perfect length would be like a short sword or 12" to 15" length.
?
All depends!!!!!